The present invention is related to solid-state switching devices for distributing alternating current (AC) power, and in particular to leakage reduction circuits for minimizing AC leakage current in solid-state switching devices.
Solid-state AC switches are commonly used in place of mechanical relays to distribute power from a source to a load. Solid-state AC switches typically include a pair of solid-state switching devices (SSSDs) connected in series with one another. Each SSSD includes a control terminal and at least two controlled terminals. A control signal provided to the control terminal dictates whether the SSSD is On or Off. When the SSSD is On, the device allows power provided at a first controlled terminal to be supplied to a second controlled terminal. When the SSSD is Off, the device prevents power provided at a first controlled terminal from being supplied to a second controlled terminal. However, most SSSDs are uni-directional, meaning that they allow current to flow in one direction even when Off. For this reason, a solid-state AC switch requires a pair of solid-state switching devices connected in a back-to-back configuration to block both the positive half-cycle and negative half-cycle of the AC input power.
Leakage current is the result of some current being allowed to flow even when both of the series-connected SSSDs are Off. This is a result of parasitic capacitances associated with each SSSD that charge/discharge during the half-cycles of the AC waveform. For example, the junction capacitance associated with the SSSDs allow energy to be stored during a half-cycle of the AC waveform, and as the AC voltage decreases toward the zero crossing, the junction capacitance is discharged, resulting in undesirable leakage current flowing through the SSSD.